1. Field of the Invention
The invention relates to an antenna coupler for testing a mobile-radio device.
2. Discussion of the Background
For the testing of mobile-radio devices, it was formerly conventional to provide a separate connection to the mobile-radio device, by means of which the mobile-radio device is connected to test device. However, this has the disadvantage, that only a part of the hardware of the mobile-radio device is used in the test. Accordingly, the transmission of the signals is not implemented, for example, via the radio interface, but via a cable-bound connection. Antenna couplers were developed to remedy this disadvantage. The antenna couplers use a capacitive or inductive coupling in order to transmit signals between the mobile-radio device and the test device connected to the antenna coupler for the implementation of the test. One problem in this context is that different mobile-radio devices operate in different frequency ranges. This generally requires the arrangement of several antennas within the coupler, wherein an accurate positioning of the mobile-radio device relative to the respective antennas must be implemented because of the selective behaviour of the antennas. To resolve this problem, the use of a spiral-shaped, structurally flat antenna is known from DE 10 2004 033 383 A1. This has improved coupling properties and can, in particular, be used in a broadband manner. The spiral-shaped antenna structure can be provided, for example, by strip conductors formed on a printed-circuit board. With the proposed spiral antenna for an antenna coupler, it is problematic that, with conventional antennas, within the near field, a strong interaction occurs between the radiating element, that is, the spiral antenna, and the metallic, radiating antenna part in the mobile-radio device.